ASoC: soc-pcm: Fix and cleanup DPCM locking

The existing locking for DPCM has several issues
a) a confusing mix of card->mutex and card->pcm_mutex.
b) a dpcm_lock spinlock added inconsistently and on paths that could
be recursively taken. The use of irqsave/irqrestore was also overkill.

The suggested model is:

1) The pcm_mutex is the top-most protection of BE links in the FE. The
pcm_mutex is applied always on either the top PCM callbacks or the
external call from DAPM, not taken in the internal functions.

2) the FE stream lock is taken in higher levels before invoking
dpcm_be_dai_trigger()

3) when adding and deleting a BE, both the pcm_mutex and FE stream
lock are taken.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
[clarification of commit message by plbossart]
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Reviewed-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Link: https://lore.kernel.org/r/20211207173745.15850-4-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>

include/sound/soc.h

@@ -893,8 +893,6 @@ struct snd_soc_card {
 	struct mutex pcm_mutex;
 	enum snd_soc_pcm_subclass pcm_subclass;
 
-	spinlock_t dpcm_lock;
-
 	int (*probe)(struct snd_soc_card *card);
 	int (*late_probe)(struct snd_soc_card *card);
 	int (*remove)(struct snd_soc_card *card);

sound/soc/soc-core.c

@@ -2315,7 +2315,6 @@ int snd_soc_register_card(struct snd_soc_card *card)
 	mutex_init(&card->mutex);
 	mutex_init(&card->dapm_mutex);
 	mutex_init(&card->pcm_mutex);
-	spin_lock_init(&card->dpcm_lock);
 
 	return snd_soc_bind_card(card);
 }